// 公共方法
 
// 生成图片
const imageFromPath = function (src){
    let img = new Image()
    img.src = './images/'+src
    img.className = 'bullet'
    return img
}
// 原生动画参数
const keyframesOptions = {
    iterations: 1,
    iterationStart: 0,
    delay: 0,
    endDelay: 0,
    direction: 'alternate',
    duration: 3000,
    fill: 'forwards',
    easing: 'ease-out',
  }